Study Cites Benefits but Caution Regarding Iodine

by | Oct 19, 2016 | 2016, Iodine, Minerals, Thyroid

Written by Greg Arnold, DC, CSCS. China’s 16- year program of food fortification with iodine to reduce iodine insufficiency was significantly effective in four cities that had inadequate iodine levels prior to the intake of iodine fortified food; however, the program significantly increased thyroid disorders in 6 cities that already had adequate iodine intake levels.

Iodine is a trace element that is naturally present in foods like seaweed, cod, and milk, added to other foods like salt, and available as a dietary supplement 1. Iodine is crucial to proper function of the thyroid gland and is an essential component of two thyroid hormones: thyroxine (T4) and triiodothyronine (T3). The thyroid regulates metabolism and also important chemical reactions in the body 2 as well as being needed in infants for proper bone and nervous system development 3. The current recommendations from the National Institutes of Health for iodine range from 90 micrograms per day in children 1-8 years of age to 290 micrograms per day in lactating women 1.

Because of iodine’s importance in the body, deficiency can cause significant problems. These include short-term illnesses like goiter 4 and long-term conditions such as mental retardation 5, stunted growth and both physical neurological abnormalities 6. As a result, fortifying foods with iodine became a public health campaign in the 1920’s and has been such a success that iodine fortification of foods like salt are still done even though the program has always been mandatory 7.

Many countries, including China, have followed in the United States’ footsteps with iodine fortification. In the 1970s, it was estimated that 425 hundred million people lived in iodine-deficient regions, 35 million had goiter, and 250,000 had cretinism 8. As a result, a program mandating fortifying salt with iodine was introduced in 1996 and lasted 16 years. Over the next two decades, China was able to significantly reduce iodine deficiency diseases 9.

Now research has revisited China’s iodine fortification program and has discovered this program was not without some drawbacks. In a 2016 study 10, researchers studied 15,008 Chinese adults from 10 cities in eastern and central China. They obtained blood and urine samples to measure for several factors of iodine levels and thyroid health. The researchers found that four of the 10 cities were classified as having “more than adequate intake” of iodine (urinary iodine concentrations of 239.5 micrograms/Liter) and this led to an increase in thyroid disorders that result from having too much iodine.

Specifically, compared to the six cites with “adequate iodine intake” (urinary iodine concentration of 172.8 micrograms/L), the four cities with “more than adequate iodine” intake saw higher rates of:

  • Clinical hyperthyroidism (1.1% vs. 0.8%, p = 0.033)
  • Graves’ disease (0.8% vs. 0.5%, p = 0.019) also significantly increased in MTAII cities.
  • Thyroid nodules (12.8% vs. 2.78%, p = 0.001)
  • Subclinical hypothyroidism (16.7% vs. 3.22%)

The four cities with more than adequate iodine intake also had much lower rates of Goiter (2.9% vs. 5.02%, p = 0.001).

For the researchers, “the iodine nutrition status in China has greatly improved, and the aim of eliminating iodine deficiency has been successfully achieved. However, the prevalence and spectrum of thyroid disorders has increased, reflecting possible adverse effects of increased iodine intake” and that “the importance of ongoing monitoring of the population iodine status and keeping the iodine intake at an optimal and safe level must be emphasized.”

Source: Shan Z. Iodine Status and Prevalence of Thyroid Disorders After Introduction of Mandatory Universal Salt Iodization for 16 Years in China: A Cross-Sectional Study in 10 Cities. Thyroid 2016 Aug;26(8):1125-30. doi: 10.1089/thy.2015.0613. Epub 2016 Jul 22

© Mary Ann Liebert, Inc.

Posted October 19, 2016.

Greg Arnold is a Chiropractic Physician practicing in Hauppauge, NY.  You can contact Dr. Arnold directly by emailing him at PitchingDoc@msn.com or visiting his web site at www.PitchingDoc.com.

References:

  1. NIH. Iodine.
  2. In: Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington (DC)2001.
  3. WHO U. International Council for the Control of Iodine Deficiency Disorders. Assessment of iodine deficiency disorders and monitoring their elimination: a guide for programme managers, 3rd edn Geneva: World Health Organization. 2007.
  4. Council NR. Health implications of perchlorate ingestion. National Academies Press; 2005.
  5. Network IG. Iodine Deficiency.
  6. Zimmermann MB. Iodine deficiency. Endocr Rev. 2009;30(4):376-408.
  7. Dasgupta PK, Liu Y, Dyke JV. Iodine nutrition: iodine content of iodized salt in the United States. Environ Sci Technol. 2008;42(4):1315-1323.
  8. Ma T, Guo J, Wang F. The epidemiology of iodine-deficiency diseases in China. Am J Clin Nutr. 1993;57(2 Suppl):264s-266s.
  9. Zimmermann MB, Andersson M. Update on iodine status worldwide. Curr Opin Endocrinol Diabetes Obes. 2012;19(5):382-387.
  10. Shan Z, Chen L, Lian X, et al. Iodine Status and Prevalence of Thyroid Disorders After Introduction of Mandatory Universal Salt Iodization for 16 Years in China: A Cross-Sectional Study in 10 Cities. Thyroid. 2016;26(8):1125-1130.